- CORS Error Explained: "Blocked by CORS Policy" and How to Fix It
What 'has been blocked by CORS policy: No Access-Control-Allow-Origin header' means, how preflight requests work, and the server headers that fix it for real. - Fix "[email protected]: Permission denied (publickey)"
Fix GitHub's 'Permission denied (publickey)': test with ssh -T, read ssh -vT output, load your key into the agent, check it's on your account, or use HTTPS. - Fix pip "error: externally-managed-environment" (PEP 668)
Why pip says 'externally-managed-environment' on Linux and Homebrew, and the real fixes: a venv, pipx or the distro package, not --break-system-packages. - How to Fix "Port Already in Use" (Windows, macOS, Linux)
Find which process holds a port and free it: netstat, Get-NetTCPConnection, lsof and ss commands, plus what EADDRINUSE and WinError 10048 actually mean. - Git "Detached HEAD" State: What It Means and How to Fix It
Detached HEAD means Git has checked out a commit, not a branch. Why it happens, how to keep commits made there with git switch -c, and how to get back to a branch. - Git Merge vs Rebase: What Each Does to Your History
Merge keeps history as it happened with a merge commit; rebase replays your commits for a straight line. Commit graphs, when to use each, and git pull --rebase. - How to Undo the Last Git Commit (reset, amend, revert)
Undo your last Git commit with git reset --soft, --mixed or --hard, fix it with --amend, or use git revert when the commit is already pushed to a shared branch. - How to Read a Stack Trace (Python Traceback and Node.js)
Read a Python traceback from the bottom up and a Node.js stack trace from the top down, find the first frame in your code, and tell your code from library frames. - HTTP Status Codes Explained: The Ones You Actually See
What 200, 201, 204, 301, 302, 304, 400, 401, 403, 404, 405, 409, 422, 429, 500, 502, 503 and 504 mean, plus 401 vs 403 and 502 vs 504, from RFC 9110. - JSON vs YAML vs TOML: Same Config, Three Formats Compared
One config file in JSON, YAML and TOML, with the gotchas that bite: YAML's Norway problem and indentation, TOML tables, JSON's lack of comments. When to pick each. - Python Virtual Environments (venv): Create, Activate, Use
Create a Python venv, activate it in Windows cmd, PowerShell (including the execution policy error), macOS and Linux, save requirements.txt, and keep it out of Git.
Coding
Git, Python, JavaScript, APIs and the errors developers hit every day.